Corrosion Resistance of Alloys of the Al–Cu–Fe–(Si, B) System in Mineralized Saline and Acid Solutions

Abstract

We study the influence of alloying with 4–7 at.% Si and/or 1–3 at.% B on the corrosion behavior of Al– Cu–Fe quasicrystalline alloys in the solutions of HCl, H2SO4 , HNO3, and H3PO4 (pH 1.0) acids and in 3.0 M NaCl and 0.2 M Na2SO4 (pH 7.0) solutions of salts. We use the methods of quantitative metallography, electron microscopy, and gravimetric analysis. It is shown that the studied alloys corrode especially intensely in the solutions of HCl and H2SO4 acids, while the least intense corrosion is observed in a solution of HNO3. The corrosion resistance in acids increases as the content of phases enriched with iron in the structure of alloy decreases. Corrosion mainly occurs in the areas with the λ -Al13Fe4 phase or ψ –λ and ψ –(τ, η, θ) interfaces. As compared with the acid solutions, the alloys corrode much slower in saline solutions. In these solutions, we also observe the process of selective corrosion of iron from the Al–Cu–Fe–(Si, B) alloys but the dissolution of phases is more uniform than in acid solutions. On the surfaces of alloys, we observe the formation of the areas of brown rust and pits. The bottoms of the pits are covered with porous copper layers. For the major part of samples and pits, their corrosion in NaCl solutions is stronger than in Na2SO4 solutions. The positive influence of alloying with Si or/and B on the corrosion resistance of alloys is revealed. The compositions of alloys with the highest corrosion resistances are determined. The Al55Cu25Fe12Si7B1 and Al53Cu25Fe12Si7B3 alloys are recommended for operation in acid and saline solutions, respectively.